Thermally responsive switch with a bimetal latch operating at right angles to the movement of the contacts



Dec. 10, 1968 H. GROSSE-BRAUCKMANN 3,416,117

THERMALLY RESPONSIVE SWITCH WITH A BIMETAL LATCH OPERATING AT RIGHT ANGLES THE MOVEMENT OF THE CONTACTS F" d Oct. 14, 1966 Fllg.

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4 LAJQ g Z //AQ L; L /3 lnven/ar: Helmui Grosse-Brauckmunn AHo rners United States Patent 3,416,117 THERMALLY RESPONSIVE SWITCH WITH A BI- METAL LATCH OPERATING AT RIGHT ANGLES TO THE MOVEMENT OF THE CONTACTS Helmut Grosse-Brauckmann, Hameln, Germany, assignor to Licentia Patent-Verwaltungs-G.m.b.H., Frankfurt am Main, Germany Filed Oct. 14, 1966, Ser. No. 586,722 Claims priority, application Germany, Oct. 15, 1965, L 51,910 9 Claims. (Cl. 337-358) The present invention relates to a switch and, more particularly, to a temperature responsive switch.

It is the primary object of the present invention to provide a temperature responsive switch which is simple and of rugged construction, which incorporates but few parts, which can easily be assembled, and which is fool-proof, in the sense that the switch will open when a given temperature is exceeded even though the operator may try to hold the switch in closed position and which switch cannot be closed, despite the efforts of the operator, when the temperature in question is still greater than that at which the switch is intended to interrupt an electric circuit, and which switch, finally can be opened manually whenever desired.

With the above object in view, the present invention resides, basically, in a switch comprising a housing in which the stationary contact is arranged. Also provided is a leaf spring one of whose ends is secured to the housing, this leaf spring carrying a movable contact which, with the leaf spring, is movable into and out of engagement with the stationary contact. One end of a bimetallic strip is attached to the leaf spring, this bimetallic strip lying generally in a plane parallel to the direction in which the leaf spring moves, the bimetallic strip being so arranged that, under the influence of heat, it flexes in a direction at right angles to the direction in which the leaf spring moves. An actuating element is provided which is mounted for movement so as to engage an edge of the free end of the bimetallic strip to move the sameand with the leaf spring and the movable contact-from open to closed position whenever the actuating element is actuated, the arrangement of the parts being such that when the bimetallic strip is flexed under the influence of the heat, the free end of the bimetallic strip moves out of the sphere of influence of the actuating element. Finally, means are provided for interlocking the actuating element and the bimetallic strip while the switch is in its closed position and the bimetallic strip is not flexed under the influence of heat.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a sectional view of one embodiment of a switch according to the present invention.

FIGURE 2 is a sectional view taken on line 22 of FIGURE 1.

FIGURE 3 is a fragmentary sectional view showing a modified embodiment of a switch according to the present invention.

Referring now to the drawing and first to FIGURES 1 and 2 thereof, the same show an elongated switch housing 1 having arranged within it a bimetallic strip 2 secured to a leaf spring 3. The leaf spring 3 is L-shaped and has a short leg 3a at which the leaf spring is secured to one of the end walls of the switch housing. The length of the leaf spring 3 is more than half the length of the switch and carries at a point spaced from the bend 3' and preferably at its free end a movable contact 4 which coacts with a stationary contact 5 carried by an elongated contact strip 6. The bimetallic strip 2 is connected to the long, free leg of the leaf spring 3 at a point near the bend 3' of the leaf spring. The leaf spring is so arranged that when it is in its unstressed condition, the contacts 4 and 5 are maintained in spaced apart relation so that the switch is in its open position, while the bimetallic strip 2 lies in a plane which is coincident with or parallel to the plane in which the leaf spring 3 moves in order to move the switch between its open and closed positions.

The switch further comprises a heater winding 7 which is wound about the bimetallic strip 2, one terminal of the heater being electrically conductively connected with the bimetallic strip while the other end of the heater winding 7 is connected with a further contact strip 8.

The edge 2' of the bimetallic strip 2-this being the edgeopposite the edge 2" that faces the leaf spring 3-is provided, near the free end of the bimetallic strip 2, with a locking recess 2a for receiving a projection 9a of an actuating element such as a push button 9 which itself is slidably arranged between the walls of the housing 1 for reciprocatory movement therein, the button 9 running through a housing extension 1a. As shown in FIGURE 1, the projection 9a transitions into a bevelled end 9b, the same having a configuration corresponding to that of a bevelled edge 2b of the bimetallic strip 2. The push button 9 further carries a pin 10 which slides in an inwardly extending housing projection 1b, the pin 10 being surrounded by a return spring 11 which is interposed between the projection 1b and the underside of the button 9 so as continuously to urge the push but-ton 9 away from the bimetallic strip 2, the projection 1b also serving to limit the downward movement of the button 9. As also shown in FIGURE 1, the push button 9 is provided with a slot 12 which extends parallel to the bimetallic strip 2 when the same is cold, i.e., when the strip is not flexed under the influence of heat. Finally, FIGURE 1 shows an adjusting screw 13 for adjusting the position of the leaf spring 3.

The switch is shown in its closed position, the bimetallic strip being unflexed and therefore straight and holding the push button 9 in its depressed position in which the projection 9a is held within the locking recess 2a. This locks the switch in its closed position, the spring 3 being in its stressed condition. Similarly, the return spring 11, being compressed between the projection 1b and the underside of the button 9, is in its stressed condition. If, now, due to an overload current flowing through the heater winding 9, the bimetallic strip is heated up, the same will flex in the direction shown by the arrow 14. In the course of this flexing, the locking recess 2a slides away from the projection 9a of the push button 9 and the upper end of the bimetallic strip 2 comes into alignment with the slot 12 and is in fact pressed into the slot under the influence of the tensioned leaf spring 3. The movable contact 4 wi l thus move away from the stationary contact 5 and the push button 9 is forced upwardly under the influence of the return spring 11. In the course of the upward movement, the lower end, due to the bevelled end 9b, moves out of the effective sphere of influence of the bimetallic strip 2. The bevelled end 9b lies just in front of the free end of of the bimetallic strip which has swung to the right, as viewed in FIGURE 1.

The switch cannot be closed again until the bimetallic strip has cooled to the point where it is once more straight. Any attempt to close the switch before the bimetallic strip has cooled down sufliciently will be to no avail inasmuch as the free end of the bimetallic strip is still in the region of the slot 12 so that all that happens when the push button 9 is depressed is that the bimetallic strip 2 comes to lie partly in the slot 12. If, on the other hand, the bimetallic strip has cooled down sufliciently, the bevelled end 9b of the push button 9 slides along the bevelled edge 2b of the bimetallic strip 2 and returns the bimetallic strip into the position shown in FIGURE 1, thereby closing the contacts 4, 5. The projection 9a once more comes to lie in the locking recess 2a.

It will be appreciated that, upon heating up of the bimetallic strip 2, the switch will open automatically even if the push button 9 is kept in its depressed position, because the bimetallic strip 2 is still free to flex and to come into alignment with and ultimately slide into the slot 12, thereby allowing the contacts 4, to separate.

Moreover, despite the self-locking feature, the switch can be opened manually simply by so fashioning the end of the push button 9 which extends out of the housing 9 as to allow the button to be pulled out. This frees the bimetallic strip and allows the spring 3 to move to the right, as viewed in FIGURE 1, thereby to move the contact 4 away from the contact 5.

One of the advantageous characteristics of a switch according to the present invention is that the leaf spring 3 carrying the movable contact does not require any complicated mounting. It suflices if the leaf spring is wedged or riveted to the end wall of the housing, which immediately fixes the direction in which the leaf spring can move, there being no need to provide any abutments or other means which prevent the leaf spring from deflecting in any direction other than the intended direction. Furthermore, the switch incorporates relatively few individual parts, and even those parts can be manufactured by simple processes, such as by stamping and bending. The push button, too, can easily be made by conventional extrusion or molding techniques which likewise do not require any complicated pieces of equipment. In practice, the push button will be metallized in the region of the locking projection, and even this metal coating can be provided by pressing or injecting the same onto the push button. Yet another significant advantage is that, thanks to the few parts, the switch as a whole is very compact and is easily assembled.

The switch can be simplified even more by making the push button as shown in FIGURE 3. Here, one leg of the push button 90 is provided with bore 16 within which there is a metal screw 15 which may be provided with a self-cutting thread so that the screw 15 is firmly anchored in the push button 90. The screw 15 has a hardened and polished end 15a which extends into the slot 120 and which serves to lock the push button to the bimetallic strip 2, this screw 15, 150, thus taking the place of the projection 9a described in conjunction with the embodiment of FIGURES 1 and 2. The slot 120 is sufficiently wide to enable the bimetallic strip 20 to flex, under the influence of heat, so as to come out of the sphere of influence of the screw end 15a.

The embodiment shown in FIGURE 3 represents an improvement over that shown in FIGURES 1 and 2 in that the metallized coating on the push button can be dispensed with, as can be the adjustment 13 shown in FIGURE 2 inasmuch as the screw 15, 15a also serves to adjust the switch. In practice, the housing (not shown in FIGURE 3) is provided with an opening which is in alignment with the screw 15 so as to allow the same to be adjusted from the outside. After the adjustment has been made, the screw can be coated with a lacquer.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims. For example, in place of the push button, the actuating element of the switch can be constituted by a pivoted lever one of whose arms interlocks with the locking recess of the bimetallic strip.

Nor is the present invention limited for use as a current.

overload switch, i.e., a switch which opens as the result of an overload current flowing through the winding 7 surrounding the bimetallic strip 2, in that the bimetallic strip 2 can be responsive to ambient temperature in which case the switch will open when the surrounding air exceeds a predetermined temperature.

What is claimed is:

1. A switch comprising, in combination:

(a) a housing;

(b) a stationary contact arranged in said housing;

(c) a leaf spring having one end secured to said housing and carrying, at a point spaced from said one end, a movable contact which, with said leaf spring, is movable into and out of engagement with said stationary contact;

((1) a bimetallic strip lying generally in a plane parallel to the direction in which said leaf spring moves, said bimetallic strip, under the influence of heat, flexing in a direction at right angles to the direction in which said leaf spring moves, one end of said bimetallic strip being secured to said leaf spring, the other end of said bimetallic strip being a free end;

(e) an actuating element carried by said housing and mounted for movement to engage an edge of said free end of said bimetallic strip to move the same and with it said leaf spring and said movable contact from open to closed position upon actuation of said actuating element, said free end of said bimetallic strip, when the latter is flexed under the influence of heat, moving out of the sphere of influence of said actuating element; and

(f) means for interlocking said actuating element and said bimetallic strip while the switch is in its closed position and said bimetallic strip is not flexed under the influence of heat.

2. A switch as defined in claim 1 wherein said actuating element is a push button mounted for reciprocatory movement in said housing.

3. A switch as defined in claim 2 wherein said locking means are constituted by a locking recess on an edge of said free end of said bimetallic strip and a locking projection on said push button.

4. A switch as defined in claim 3 wherein said free end of said bimetallic strip and said push button are provided with oppositely directed bevelled surfaces which interengage each other when said push button is moved toward said bimetallic strip.

5. A switch as defined in claim 3 wherein said push button is provided with a slot which extends in the plane occupied by said bimetallic strip when the same is not flexed under the influence of heat.

6. A switch as defined in claim 3, further comprising means for continuously urging said push button away from said bimetallic strip.

7. A switch as defined in claim 2 wherein said push button is provided with a slot which receives said bimetallic strip, said slot being sufficiently wide to contain said bimetallic strip both when the same is and is not flexed under the influence of heat, and wherein said locking means are constituted by a locking recess on an edge of said free end of said bimetallic strip and a screw carried by said push button and having an end portion extending into said slot a distance suflicient to lie in said locking recess when said strip is not flexed under the influence of heat.

8. A switch as defined in claim 7 wherein said screw has a self-cutting thread and is threaded into said push button.

9. A switch as defined in claim 7 wherein said screw extends at right angles to the direction of movement of said push button and all but said end portion of said screw is screwed into said push button.

(References on following page) 3,416,117 5 References Cited UNITED STATES PATENTS 2,335,081 11/1943 Platz 200116 2,743,333 4/1968 Epstein 200-113 5 3,141,941 7/1964 Dew 200-116 337-362 6 BERNARD A. GILHEANY, Primary Examiner. R. COHRS, Assistant Examiner. 

1. A SWITCH COMPRISING, IN COMBINATION: (A) A HOUSING; (B) A STATIONARY CONTACT ARRANGED IN SAID HOUSING; (C) A LEAF SPRING HAVING ONE END SECURED TO SAID HOUSING AND CARRYING, AT A POINT SPACED FROM SAID ONE END, A MOVABLE CONTACT WHICH, WITH SAID LEAF SPRING, IS MOVABLE INTO AND OUT OF ENGAGEMENT WITH SAID STATIONARY CONTACT; (D) A BIMETALLIC STRIP LYING GENERALLY IN A PLANE PARALLEL TO THE DIRECTION IN WHICH SAID LEAF SPRING MOVES, SAID BIMETALLILC STRIP, UNDER THE INFLUENCE OF HEAT, FLEXING IN A DIRECTION AT RIGHT ANGLES TO THE DIRECTION IN WHICH SAID LEAF SPRING MOVES, ONE END OF SAID BIMETALLLIC STRIP BEING SECURED TO SAID LEAF SPRING, THE OTHER END OF SAID BIMETALLIC STRIP BEING A FREE END; (E) AN ACTUATING ELEMENT CARRIED BY SAID HOUSING AND MOUNTED FOR MOVEMENT TO ENGAGE AN EDGE OF SAID FREE END OF SAID BIMETALLIC STRIP TO MOVE THE SAME AND WITH IT SAID LEAF SPRING AND SAID MOVABLE CONTACT FROM OPEN TO CLOSED POSITION UPON ACTUATION OF SAID ACTUATING ELEMENT, SAID FREE END OF SAID BIMETALLIC STRIP, WHEN THE LATTER IS FLEXED UNDER THE INFLUENCE OF HEAT, MOVING OUT OF THE SPHERE OF INFLUENCE OF SAID ACTUATING ELEMENT; AND (F) MEANS FOR INTERLOCKING SAID ACTUATING ELEMENT AND SAID BIMETALLIC STRIP WHILE THE SWITCH IS IN ITS CLOSED POSITION AND SAID BIMETALLIC STRIP IS NOT FLEXED UNDER THE INFLUENCE OF HEAT. 